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Re: TECH: use fetchmail algorithm to select header address to verify

2004-09-06 23:08:22

Yakov Shafranovich <research(_at_)solidmatrix(_dot_)com> writes:

Now, I am an SMTP developer and after reading the RFC I want to find out 
who put the original message into the mail system. In order to determine 
the actual party who sent the original message according to the RFC I 
would have to look for the "Sender" field. If it is not present, then 
the "From" header is used since the RFC states (section 3.6.2) "if the 
originator of the message can be indicated by a single mailbox and the 
author and transmitter are identical, the "Sender:" field SHOULD NOT be 
used." However, since the same RFC states that "Resent" fields are 
basically the same as the regular "Sender" and "From" fields in cases 
where the email is forwarded and re-introduced into the email system, I 
would have to parse "Resent-Sender" first, then "Resent-From", and only 
after that the regular "Sender" and "From" fields.

And by the same RFC, some of the situations which some discussion on
this last has suggested that Resent-* headers might be inserted (by
the MTA) are not valid usage of those fields. If the mail is
originally addressed to me(_at_)alumni(_dot_)org and is then forwarded to my
"real" address me(_at_)example(_dot_)com, then it is valid for alumni.org to add
Resent-* headers. But if example.com sends mail via an ISP or MSP
isp.com then it is not valid (as some have suggested here to enable
the PRA to match) for isp.com to add Resent-* headers to all outgoing
mail from its customers.


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